In certain technical fields such as gas turbine engine technology or combustor technology where the engines or combustors are required to be more efficient, temperatures within the engine or combustor have continued to rise. However, in order to maintain the ability to operate at these increasing temperatures, the metal components of the engine or combustor which are directly exposed to the increased temperatures have been protected by a thermal barrier coating (TBC) having a ceramic layer which insulates the components.
Typically, the thermal barrier coating includes a ceramic top coat made of stabilized zirconia and disposed on an aluminide or MCrAlY bond coat, with M selected from a group consisting of iron, cobalt, nickel, and mixtures thereof.
The ceramic top coat may have a columnar grain microstructure for allowing the columnar grains to expand and contract without developing stresses that could cause spalling.
The ceramic top coat is usually applied by electron-beam physical vapor deposition (EB-PVD) or plasma spraying, two coating processes which require a certain distance between the substrate to be coated and the source of ceramic material. In other words, it is difficult to apply EB-PVD or plasma sprayed coatings to a metal article having a narrow or complicated internal passage to be coated with the ceramic coating.